The present invention relates to heated chambers, and is more particularly, but not exclusively concerned, with the wall arrangements of fluidised bed combustion chambers and the like.
The walls of any heated chamber expand when combustion takes place in the chamber and the walls are normally provided with expansion gaps enabling them to expand as their temperature rises.
Attempts have been made to fill these expansion gaps with a resilient packing material which will withstand the heat of the combustion taking place in the chamber and will prevent material in the chamber passing into the gaps.
Fluidised bed combustors and furnaces employ a bed of inert material, usually sand through which air is passed to agitate and keep the bed in motion. The inert material of the bed warms during combustion and aids and supports combustion of materials fed thereto.
In fluidised bed combustors and furnaces it has been found that the inert material forming the bed acts as an abrasive wearing away packing material in the expansion gaps. As soon as the packing material has worn away the inert material percolates into the gaps filling them and preventing expansion of the walls.
Arrangements for filling the expansion gaps with particularly hard materials, such as ceramic fibers, have proved ineffective as it has been found that the inert material of the bed percolates into the interstices of the fiber, fills the gaps and prevents expansion of the walls.
If the walls cannot properly expand when the heated chamber warms they may buckle and fail.
An object of this invention includes the provision of wall arrangement alleviating or meeting this problem.
One aspect of the present invention provides a wall arrangement for a heated chamber, said walls having gaps enabling expansion of the walls when the temperature of the chamber is increasing and including means for preventing inert material packing said gaps so as to prevent expansion of said walls.
Said means may include means for promoting movement, in the gaps, of any of said material that falls therein, and may include means for injecting gas into the or each gap to maintain inert material falling into said gap in motion. The gas may be air, flue-gas or a furnace atmosphere.
A fluidised bed combustor or furnace embodying the invention provides that said means include one or more sparge pipes individually located adjacent respective ones of a plurality of expansion gaps and arranged to direct air thereinto. Each said sparge pipe preferably extends through an outer casing of the combustion chamber and lies immediately behind its associated expansion gap formed in the lining of said combustion chamber.
Each said sparge pipe preferably lies between the refractory lining of a fluidised bed combustion chamber and the casing of the fluidised bed tank and acts to support said refractory lining relative to the outer casing of the combustion chamber.
Further aspects of the present invention provide a fluidised bed combustion chamber or furnace as defined above, further including means for supplying air to the or each said sparge pipe only whilst said combustion chamber is below its normal operating temperature.